1. Field of Invention
The present invention relates to devices for distributing irrigation water to crops, lawn areas, and the like. It relates, more particularly, to such devices equipped with rotating sprinkler heads.
2. Description of Prior Art
It is known in the prior art to provide a water distributing device based on a rotary sprinkler head whose rotation is derived from the internal energy of the pressurized water passing therethrough. Most of these devices of the prior art are restricted, inherently, to a distribution pattern corresponding to a circle whose center is the location of the sprinkler head and whose radius corresponds to the reach of the jet, or jets, issuing from its orifices. However, use of such devices may necessitate the over-lapping of sprinkled areas and the precipitation of undesired areas in order to irrigate a non-circular shaped area.
There have also been proposed variations on these devices which would permit the shape of the irrigated area to be varied from a circular one, typically to a square or rectangle, and even an arbitrary pattern.
Such devices have not met with commerical success due to their poor performance, high cost, unreliable operation, or a combination of such factors.
A prior art device described in U.S. Pat. No. 3,884,416 issued May 20, 1975 to Michael L. King appears to produce a desired irrigation pattern by means of an orifice plate having rectangular passages and a port plate having rectangular ports. The radial reach of the water is varied depending upon the mutual overlap between the radially offset ports. The primary disadvantage of this approach lies in the small port size required to vary the water flow. Small holes tend to get plugged up with particles, thereby requiring frequent disassembly and cleaning. Another disadvantage is in the requirement of an adjustable device for obtaining a constant angular velocity. This adjustment has to be made for each change in water pressure.
Another prior art device described in U.S. Pat. No. 4,819,875 issued Apr. 11, 1989 to Glenn I. Beal appears to produce an irregular watering pattern by means of a throttling device for controlling water flow to the sprinkler in accordance with the rotary position of the sprinkler relative to the housing. No attempt was made to control the angular velocity of the sprinkler to a constant.
Both of the above prior art allow the water supply pressure to force the rotating sprinkler against its washers creating a large rotating frictional force. This force is greater when the flow is restricted due to the increased back pressure. This makes it nearly impossible to achieve a constant angular velocity with conventional impact sprinklers.
All the devices heretofore known suffer from a number of disadvantages:
(a) A complicated device makes it expensive to manufacture.
(b) If water flow is not straight through, unreliable operation occurs from small holes getting plugged, which requires disassembly and cleaning.
(c) Angular velocity is not constant creating a non-uniform water distribution.
(d) Standard impact sprinklers would need to be modified to achieve the desired results.